Particularly in the automobile sector, the number of potential areas of use for magnetic field sensors is growing; in particular, magnetic field measurement can be used, inter alia, for the non-contact, low-loss and potential-free measurement of currents. An example is the determination of electrical operating parameters of generators and electric drives, such as the current intensity, the current direction and the like of the three phases of a three-phase generator.
Presently, it is general state of the art to measure the magnetic field or its strength using magnetic-field sensors such as Hall sensors, bipolar magneto-transistors, magnetoresistive resistors, lateral magnetic field-effect transistors (MagFET structures) and the like. In general, the sensors are produced as autonomous components, and must be mounted separately in the application. This may result in considerable additional integration costs for system manufacturers.
Sturdy and inexpensive sensors of small size which measure the magnetic field in general, and particularly those magnetic fields produced by currents through conductors, as accurately as possible are desirable especially for the automobile sector, but not exclusively for it. The present invention describes a new type of sensor element which is based on the known trench MOS semiconductor technology, and therefore may be produced relatively easily by existing processes or integrated into them. Moreover, according to the invention, the possibility is provided of producing a new type of intelligent circuit breaker with integrated current sensor, particularly on a single substrate, i.e. on a single chip.
The essence of the invention is to use the vertical MOS channel of a trench MOSFET for sensing the magnetic field. In the presence of a magnetic field, the Lorentz force deflects the moved charge carriers, and thus increases the resistance in the MOS channel. This increase in resistance leads to a source-drain current changexe2x80x94i.e. alternatively to a change in voltage in the case of an impressed predefined current through the MOS channelxe2x80x94which may be used as a measure for the strength of the existing magnetic field. By suitable structuring of the MOSFET cells, the present invention likewise provides for detecting the deflection of the charge carriers from the originally vertical current direction as a measuring signal. In contrast to planar MOS structures like, for example, in the case of MagFETs, according to the present invention, the vertical profile of the trench MOS channels makes it possible to measure magnetic fields which run parallel to the substrate surface or the chip area.
The following advantages in particular are realized according to the present invention: The device of the invention and the current sensor of the invention are based on a known trench MOS technology, which may therefore be integrated relatively simply and cost-effectively into existing semiconductor process flows. Trench-MOS processes are used by well-known semiconductor manufacturers in large quantities for field-effect transistors (FET), particularly as power transistors, and especially in the automobile sector, so that process experience and possibly even field experience is already available in this regard.
The decisive advantage of the invention is that the trench-MOS technology may be used both for implementing the switching function of the field-effect transistor and for the sensor function. The possibility is thereby created of producing a new type of intelligent field-effect transistor with integrated current sensor in a single process flow or on a single chip, i.e. in monolithic integration.
Since many applications, which rest increasingly today on MOS technology, actively control and switch, it presents itself to manufacture the sensor element needed for the current/magnetic-field measurement using the same technology. In this case, the switching and sensor functions may be combined particularly advantageously. According to the invention, the MOSFET technology is particularly usable for a high-current application such as, for example, in the electric-motor and generator field.
For applications in which currents must both be switched and actively controlled or measured, the present invention presents an optimal combination of these two functions. For example, this current is controlled via a MOSFET, i.e. a power MOSFET through which the main current flows. Because the current sensor, i.e. the current-measuring device, is integrated directly on the chip, that is, particularly the semiconductor substrate of the power transistor, the sensor element, or rather the current-measuring device, is situated in the immediate vicinity, that is, at a microscopic distance from the magnetic field generated by the main current.
In contrast with that, alternative concepts based on separate sensor elements must use costly mounting techniques in order to place the sensor element sufficiently close to the current-carrying conductor. At the same time, possible interference effects due to parasitic magnetic stray fields must be screened off as well as possible. In this context, it is particularly disadvantageous that the strength of the magnetic field to be measured generally decreases sharply with increasing distance from the current conductor carrying the current to be measured, the influence of adjacent interference fields increasing simultaneously, however. Therefore, it is particularly advantageous for a high measuring quality of the current-measuring device according to the invention that the sensor element may be placed in the immediate vicinity of the conductor through which the main current is flowing. According to the present invention, costly screening measures and possibly the use of additional flux concentrators for the magnetic field to be measured do not therefore have to be used, or must be used only to a lesser extent, which has a positive effect both on the costs and on the size of the device and the current-measuring device, respectively, of the present invention.
In the same way, the present invention provides for using the device and the current-measuring device in environments which are heavily loaded electromagnetically. To this end, it is provided according to the present invention to use a screening against parasitic interference fields, this being easy to implement by screening the entire chip, i.e. both the circuit breaker and the sensor, against external influences using a suitable packing, without at the same time impairing the coupling between the sensor and the current-carrying circuit breaker.
A further advantage of the device and of the current-measuring device according to the present invention is that the vertical MOS channels exhibit a greater sensitivity to lateral magnetic fields which run parallel to the chip surface. Here, the present invention differs in particular from the known lateral MagFET sensors, which measure magnetic fields that are vertical relative to the horizontally assumed chip surface, by change of the current direction in the MOS channel running parallel to the chip surface. Therefore, when using the present invention, it is possible to utilize the large-area chip topside itself in particular for screening measures against interference fields, while the field components necessary for the measurement penetrate laterally into the chip. The vertical trench-MOS sensor is sensitive only to these lateral field components; vertical interference fields are not taken into account.
The sensitivity of the magnetic-field sensor according to the present invention and the current-measuring device according to the present invention may be adjusted by varying the trench-cell density, the trench-cell dimensioning and the trench-cell layout. It is also possible to combine different cell geometries on one chip, to thereby implement various sensitivities simultaneously. According to the invention, it is advantageous to use such a multi-channel sensor chip in order to utilize a single sensor chip for a very large measuring range; such a large measuring range could otherwise only be covered by a combination of various sensor elements.
According to the present invention, in contrast to conventional circuit breakers, the trench-MOS cells of the device and of the current-measuring device are advantageously provided with a cell structure such that the current-sensor cells, and here in particular the trench gate wall of cells electrically coupled to one another, are all aligned orthogonally with respect to the magnetic-field component to be measured, to on one hand optimize the measuring sensitivity, and on the other hand to avoid falsification of the measurement due to magnetic-field components which are oriented differently. In the case of a linearly extending magnetic-field direction to be measured, the MOS channels along the trench walls according to the present invention are all to be aligned parallel to one another, so that all channels run orthogonally with respect to this linear magnetic-field direction.
If a plurality of magnetic-field directions or various vector components of a magnetic field are to be measured using a single chip, then for each magnetic-field component to be measured, a certain number of interconnected sensor cells are to be provided having in each case MOS channels running parallel to one another. The cell regions provided for different magnetic-field directions or vector components of a magnetic field are to be separated from one another from the standpoint of measuring and evaluation technology. The respective source-drain operating current must be supplied separately for different sensor-cell regions, to permit the separate measurement of the different magnetic-field components, and thus to avoid mixing of the measurement of the different magnetic-field components. This means that the sensor source-drain operating current must be separate at at least one location, but it may possibly be reunited at a second location; for example, according to the present invention, in the case of separate source connections, a shared drain connection is sufficient to be able to distinguish the resistance change of two different sensor cells, since in this case, the drain may be used as a common reference potential. This is particularly advantageous with respect to manufacturing, since generally only the front side of the wafer is patterned, but not the backside metallization (drain).
If curved magnetic fields, particularly annular magnetic fields are to be measured, then the orientations of the trench MOS channels are to be provided in the sensor structure in such a way that the annular magnetic lines of force always lie orthogonally with respect to the MOS channel structure, that is to say, that the walls of the trench gates are oriented such that their imaginary straight extensions essentially intersect at a common point. Generally, in the case of curved magnetic fields, the walls of the trench gates are provided in such a way that they are parallel to the local radius of curvature of the curve.
In the special case of a circle-symmetrical magnetic field, the required orthogonality of the trench gate walls with respect to the magnetic-field component to be measured is producible, for example, by cell structures running radially, i.e., running outwardly in a star shape. In this special case, the sensor cells may in fact all be evaluated, i.e., jointly wired, electrically in parallel, since although different directions of the magnetic field in space occur herexe2x80x94because the magnetic field is assumed to be roundxe2x80x94nevertheless, only a single annular magnetic-field component is measured, it being measured correctly at any location due to the orientation of the trench gate walls of the MOS channels of the sensor cells which runs outwardly in a ray shape according to the present invention.
In general, known integrated current-sensor concepts utilize a portion of the current to be measured, in order to measure, for example, the flowing current via an integrated shunt resistor. The novelty of the present invention is that the integrated current sensor utilizes the magnetic field, and is thereby advantageously decoupled from the main current to be measured.